Role of Angiotensin II in Renal Vasoconstriction with Acute Hypoxemia and Hypercapnic Acidosis in Conscious Dogs

Abstract

To evaluate the role of renin-angiotensin in the renal vasoconstriction with combined acute hypoxemia and hypercapnic acidosis preceded by acute hypoxemia, we studied eight conscious mongrel uninephrectomized dogs with chronic renal catheters and controlled sodium intake (80 mEq/24 h x 4 days). The animals were studied during combined acute hypoxemia and hypercapnic acidosis (PaO2 34 +/- 1 mm Hg, PaCo2 57 +/- 1 mm Hg, pH 7.20 +/- 0.01) preceded by 80 min of acute hypoxemia (PaO2 34 +/- 1 mm Hg) during: (a) intrarenal infusion of vehicle (n = 8); or (b) intrarenal administration of the angiotensin II antagonist [Sar1,Ala8]-AII, 70 ng kg-1 min-1 (n = 8). The combination of acute hypoxemia and hypercapnic acidosis resulted in diminished effective renal plasma flow and increased renal vascular resistance during intrarenal vehicle infusion. Intrarenal [Sar1,Ala8]-AII did not abolish the renal vasoconstriction in the initial 20 min of this combined blood gas derangement but resulted in a more prompt return of the renal vascular variables toward control levels with continuation of the blood gas derangement for an additional 20 min, suggesting a role for angiotensin in renal vasoconstriction. These observations suggest that while renin-angiotensin may not mediate the initial renal vasoconstriction in the first 20 min of combined acute hypoxemia and hypercapnic acidosis, in uninephrectomized conscious dogs, it attenuates the spontaneous recovery of renal hemodynamic variables to baseline as the blood gas derangement continues.

Re-examining Permissive Hypercapnia in ARDS

“…Acute hypercapnic acidosis has been shown to have several direct effects on renal vasculature in vivo. In conscious dogs, it reduces renal plasma flow [28][29][30] , increases renal vascular resistance 30 , stimulates robust activation of the renin-angiotensinaldosterone system 30,31 , contributes to non-osmotic release of vasopressin 29 and diminishes renal free water excretion 29 . Ischemia-induced apoptosis of rat renal tubular cells in vitro is observed when hypercapnia and hypoxemia are simultaneously present 32 .…”